While Mr Martin was not suggesting an alliance in the run-up to the 2021 election, he argued the two parties should recognise their common ground in case – as is likely – neither win a majority of seats on their own.

His intervention came as a new opinion poll showed support for the SNP has fallen sharply since last year’s Holyrood election and forecast they would win 54 seats if the election was held now, down nine and not enough for a majority.

The Survation poll for the Scottish Daily Mail said Labour would end up in second place on 30 seats, with the Tories on 24, the Liberal Democrats 13 and the Greens eight. This result would mean Holyrood would no longer have a majority of MSPs who support independence.

Scottish Labour MEP David MartinCredit:
PA

Speaking to The Herald newspaper, Mr Martin said: "We are far away from the next Holyrood elections, but I think the groundwork should be being laid now for a potential SNP-Labour coalition that to many will seem unthinkable.

“I would not quite say there is a rapprochement but there is more possibility of cooperation and working together than there has been in a long time.”

Alyn Smith, an SNP MEP, said the call was a "welcome intervention" and he did not think a coalition was “unthinkable”, arguing that the two parties already run Edinburgh City Council together.

Malcolm Chisolm, a former Labour MSP and minister, took to Twitter to express his support for the plan but a Scottish Labour spokesman said: "We do not support a deal, pact or coalition with the SNP - we plan on replacing the Nationalists as the next Scottish government."

A SNP spokeswoman said: "While we are always open to cooperating with other parties based on shared values, Labour remain obsessed with attacking the SNP instead of standing up to the Tories and their disastrous plans for an extreme Brexit."